AIM: To examine the underlying mechanisms of erlotinib-induced growth inhibition in hepatocellular carcinoma (HCC). METHODS: Erlotinib-induced alterations in gene expression were evaluated using cDNA array technology; changes in protein expression and/or protein activation due to eriotinib treatment as well as IGF-1-induced EGFR transactivation were investigated using Western blotting. RESULTS: Eriotinib treatment inhibited the mitogen activated protein (MAP)-kinase pathway and signal transducer of activation and transcription (STAT)-mediated signaling which led to an altered expression of apoptosis and cell cycle regulating genes as demonstrated by cDNA array technology. Overexpression of proapoptotic factors like caspases and gadds associated with a down-regulation of antiapoptotic factors like Bcl-2, Bcl-XL or jun D accounted for erlotinib’s potency to induce apoptosis. Downregulation of cell cycle regulators promoting the G1/S-transition and Overexpression of cyclin-dependent kinase inhibitors and gadds contributed to the induction of a G1/G0-arrest in response to eriotinib. Furthermore, we displayed the transactivation of EGFR-mediated signaling by the IGF-1-receptor and showed erlotinib’s inhibitory effects on the receptor-receptor cross talk. CONCLUSION: Our study sheds light on the understanding of the mechanisms of action of EGFR-TK-inhibition in HCC-cells and thus might facilitate the design of combination therapies that act additively or synergistically. Moreover, our data on the pathways responding to erlotinib treatment could be helpful in predicting the responsiveness of tumors to EGFR-TKIs in the future. AIM: To examine the underlying mechanisms of erlotinib-induced growth inhibition in hepatocellular carcinoma (HCC). METHODS: Erlotinib-induced alterations in gene expression were evaluated using cDNA array technology; changes in protein expression and / or protein activation due to eriotinib treatment as well as IGF-1-induced EGFR transactivation were investigated using Western blotting. RESULTS: Eriotinib treatment inhibited the mitogen activated protein (MAP) -kinase pathway and signal transducer of activation and transcription (STAT) -mediated signaling which led to an altered expression of apoptosis and cell cycle regulating genes as demonstrated by cDNA array technology. Overexpression of proapoptotic factors like caspases and gadds associated with a down-regulation of antiapoptotic factors like Bcl-2, Bcl-XL or jun D accounting for erlotinib’s potency to induce apoptosis. Downregulation of cell cycle regulators promoting the G1 / S-transition and Overexpression of cyclin-dependent kinas e inhibitors and gadds contributed to the induction of a G1 / G0-arrest in response to eriotinib. Furthermore, we displayed the transactivation of EGFR-mediated signaling by the IGF-1-receptor and showed erlotinib’s inhibitory effects on the receptor-receptor cross talk . CONCLUSION: Our study sheds light on the understanding of the mechanisms of action of EGFR-TK-inhibition in HCC-cells and thus might facilitate the design of combination therapies that act additively or synergistically. Moreover, our data on the pathways responding to erlotinib treatment could be helpful in predicting the responsiveness of tumors to EGFR-TKIs in the future.